In modern operating rooms ultraclean air is supplied through the ceiling to prevent bacteria from entering an operating wound and cause infections. Operating lamps can disturb this flow of clean air. In this paper the accuracy of some aspects of the Laminar Flow Index of operating lamps was tested. The disturbance of the airflow was determined for different shapes and sizes of operating lamps in an isothermal situation. To accomplish this, an experimental study and a simulation study of a small room with an operating lamp were performed. The infection risk was found to be proportional to the projected surface area of the lamp. Although different lamp shapes resulted in a distinctly different flow pattern in the room, this did not affect the infection risk in a significant way. Operating lamps with a projected area smaller than 0.1 m2 do not disturb the airflow at all in this particular setup.